The 2011 Fukushima earthquake resulted in a tsunami that left upwards of 20,000 people dead or missing in Japan. Since that tragedy, it has become apparent that the available reaction time to publicly broadcast warnings of impending tsunamis is very brief, e.g., less than 15 minutes. In that short time, people must leave areas that are susceptible to tsunamis, e.g., coastlines.
Although Japan is one of the most economically advanced nations, and the area affected was widely recognized as being subject to major tsunamis, Japan was still unable to marshal sufficient economic resources to place conventional tsunami shelters within reach of the general public.
Conventional tsunami shelters rely on mass and height to protect the occupants. These reinforced concrete structures are by their nature expensive to build and therefore tax public resources. Additionally, they meet public resistance due to their incompatibility with the architecture present in residential neighborhoods where they are needed the most.
As a result, conventional tsunami shelters are generally not deployed in large numbers and sufficiently close to the population to allow universal, access to such a shelter within the very short time frames provided by tsunami warning systems.